Recent study indicated the role of a gene in making it difficult for some pregnant women to quit smoking despite various dangers to the unborn baby due to smoking.

Research team from the Peninsula Medical School in Exeter and the University of Bristol studied data collected from 2,474 smokers from the Bristol area who became pregnant. Third of the study subjects carried a gene already known to make people smoke more heavily.

Data analysis revealed that women with one copy of the 'addictive gene' were 27 per cent less likely to quit whereas those with two copies were 66 per cent less likely to have given up the habit.

Dr Rachel Freathy of the Peninsula Medical School said: “We were keen to investigate whether the genetic variant that influences increased cigarette consumption also had a role to play as an extra hurdle to quitting smoking during pregnancy, and our study suggests that it does.”

Professor Tim Frayling, a senior author on the paper, said: “It is not an all or nothing situation.  It doesn't mean that if you have the gene you can't give up.”